Summary Aim. This work is aimed at gaining extended knowledge of self-destructive behaviours. Users of a social networking service devoted to people with mental disorders took part in the study. Method. The study was carried out as a voluntary web questionnaire based on clinical experience of researchers and literature. Results were summed up using standard methods of descriptive statistics. Results. 202 users of the web portal psychiatrically identified with various mental disorders participated in the study (information derived from responses given in the questionnaire). Patients afflicted by bipolar disorder and recurrent depressive disorders (72.7%) constituted the biggest group. Those previously thinking of self-harm have done it nine times more frequently, the majority under 20 years of age. These behaviours included self-mutilations (56.4%) and deliberate self-poisoning (53.5%). The biggest group of patients who declared self-harm in the past were afflicted by mood disorders (BD – 77.3%, RDD – 71.2%); however, the difference is not statistically significant. Such behaviours were reported 2.5 times more frequently (p < 0.05) by patients with identified co-occurrence of personality disorders. Thoughts of self-harm appeared not only in full-blown episodes. Regardless of the identified mental disorder, self-harming behaviours were accompanied by despondency and resignation. Approximately 10% of respondents talked about their self-harming behaviours with a psychiatrist and a psychotherapist, i.e. 1.5 times more frequently than with other people from their surrounding. Suicide attempts and completed suicides occurred much more frequently within surveyed families than in the general population. Conclusions. Self-mutilations occur mostly in patients suffering from various affective disorders. In spite of obvious restrictions of this study method, a web portal may be an effective way to collect data, for it provides fully anonymous responses.